The present invention relates to a method for preventing sucrose hydrate crystallization in a frozen material containing sucrose and preventing hygroscopic tendencies of the sucrose containing material when thawed.
Storage of foods by freezing has become so widespread that food manufacturers, processors and consumers take for granted that many types of foods can be frozen without significant damage. It has, however, long been appreciated that freezing some types of foods must be performed in a particular manner. For instance, freezing foods with a cellular matrix, such as fruits and vegetables, can damage the fruits and vegetables if the freezing and thawing steps are not performed properly. In particular, freezing disrupts cellular membranes of the fruits and vegetables.
A phenomenon that has been less widely observed is a phase change within a frozen material of substances other than water, and a precipitation of at least two types of crystals from the frozen material. One type of material that has displayed this type of crystalline formation during freezing is a material containing sucrose and water, especially when the aqueous sucrose solution is supersaturated with sucrose. This phase change is most likely to occur with materials that have high concentrations or are supersaturated with crystal-forming compounds at room temperature and subsequently frozen. Icings are an example of a material containing supersaturated crystallizable sucrose at room temperature that exhibits this phase change phenomenon during frozen storage.
An aqueous sucrose solution, considered singularly, precipitates crystals that have been identified as sucrose hydrate crystals, anhydrous sucrose crystals and ice. In particular, two hydrates of sucrose have been observed, hemiheptahydrate C.sub.12 H.sub.22 O.sub.11. 31/2 H.sub.2 O and hemipentahydrate, C.sub.12 H.sub.22 O.sub.11. 21/2 H.sub.2 O.
The sucrose hydrate crystals appear as "blooms" on the surface of the frozen sucrose-containing material. Susceptible materials include foods such as icings and fruits that contain sucrose and water. The blooms detract from the appearance of a frozen iced product such as a cake. In particular, the sucrose hydrate blooms impart a "moldy" or otherwise unacceptable appearance to the surface of the frozen material.
Once the frozen material with sucrose hydrate crystal blooms is warmed to room temperature, the sucrose hydrate crystals resolubilize into the material and cause the blooms to disappear. Once thawed, however, the material such as an icing, absorbs additional moisture from the air and from any matrix in contact with the material. "Flat" icings are particularly susceptible to this absorption. A "flat" icing is an icing that is not substantially whipped or aerated. A "flat" icing sets to hardness.
The absorption of moisture is due to a hygroscopic property of low molecular weight amorphous components in the icing. The absorption of moisture causes the material to become more fluid and to manifest a condition known as "weeping," in which the additional water absorbed by the material causes the material to become more fluid. Weeping causes the development of a wet interface between the material, such as icing, and any underlying matrix, such as cake, as water migrates from the matrix to the material.
The wet interface causes the material to become slippery and to slip off the matrix. In the case of an icing material on a cake matrix, weeping renders the icing susceptible to slipping off of the cake.
Additionally, over time, in a saturated or supersaturated material at room temperature, the additional moisture absorbed causes the excess crystalline component to solubilize completely forming a clear fluid. When the material is on the surface of a matrix, the matrix tends to absorb the fluid material, causing the material to partially or completely disappear from the surface and causing the matrix to become soggy and otherwise unacceptable. For example, when the material is icing and the matrix is cake, the icing becomes clear and patchy on the surface of the cake and the cake underlying the icing is soggy and unappealing.
The Horn et al., U.S. Pat. No. 3,676,155, issued Jul. 11, 1972, describes an icing that includes sucrose, and a levulose-dextrose mixture. This icing forms a skin that is not sticky. The skin permits an iced product to be packaged very soon after the skin is formed. The patent describes the relative amounts of sucrose and dextrose in its formulation as "critical".
The Burge et al., U.S. Pat. No. 4,037,000 issued Jul. 19, 1977, describes an icing that includes xanthan gum. This icing includes a free water content that "must not exceed 10.5% by weight."
The Cheng U.S. Pat. No. 4,135,005 issued Jan. 16, 1979, describes a freeze-thaw and heat stable icing. The icing includes a high melting point fat and a gelling system of xanthan gum and locust bean gum.
The Eckel U.S. Pat. No. 4,415,601 issued Nov. 15, 1983, describes an icing that includes powdered whey, powdered corn starch and a high melting point fat. The icing is described as a "quick hardening icing".
The Katz U.S. Pat. No. 3,532,513, issued Oct. 6, 1970, describes an aerated icing that includes a particular corn syrup preparation. The corn syrup preparation has a disaccharide to monosaccharide ratio of at least 3:1. The icing also includes a water concentration of 7 to 17 percent by weight and an emulsifier concentration of 1 to 20 percent by weight.
An article entitled "Prevention of the Growth of Sucrose Hydrates in Sucrose Syrups" by Young et al in Food Research, on pages 20-29 (1951) describes various aspects of sucrose hydrates. The reference describes a maximum rate of hydrate formation as occurring at about minus 23.3.degree. C. The reference also describes a use of an additive in a sucrose containing material. The additive includes ingredients such as maltose, dextrin and low conversion corn syrup. The reference further described the rate of sucrose hydrate growth as being greatest in solutions containing 55% sucrose.